A frequency diversity coaxial magnetron



1968 K. 0. POWELL FREQUENCY DIVERSITY COAXIAL MAGNETRON 2 Sheets-Sheet 1 Filed Oct. 15, 1965 y F I V r///7/ K II flhlv s It..

Dec. 3, 1968 P WE L 3,414,760

FREQUENCY DIVERSITY COAXIAL MAGNETRON Filed Oct. 15, 1965 2 Sheets-Sheet 2 United States Patent 3,414,760 A FREQUENCY DIVERSITY COAXIAL MAGNETRON Kenneth D. Powell, Lancaster, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 15, 1965, Ser. No. 496,351 6 Claims. (Cl. 315-3959) ABSTRACT OF THE DISCLOSURE A coaxial magnetron is described in which a small mass tuning member is provided within the coaxial cavity resonator which is driven by an elongated flexible member attached to the tuning member.

This invention relates to magnetrons and more particularly to that class of magnetrons that is referred to as a coaxial magnetron.

In the R. J. Collier et al. Patent No. 2,854,603 issued Sept. 30, 1958, there is disclosed a coaxial magnetron structure which is comprised of an inner and outer resonant system. The inner resonant system, sometimes referred to as a vane and slot system, includes a cylindrical anode together with a plurality of anode vanes radially extending inwardly therefrom. These vanes define a circumferential array of inner, anode cavity resonators. The outer resonant system is a cavity resonator defined between an outer wall and the cylindrical anode. The inner and outer systems are coupled together by a circumferential .array of spaced slots through the cylindrical anode which connects the outer resonant system with selected anode cavity resonators of the inner system. These slots are normally made to extend axially beyond the limits of the inner anode resonators for reasons including modedamping. The inner resonant system is designed to oscillate in the pi-mode, while the outer resonant system is designed to oscillate in the TE mode.

It is found in the use of coaxial magnetrons in certain radar applications that they must distinguish between the fluctuating signal of the target against a background of thermal noise, unwanted interference from ground returns, meteorological precipitation known as clutter and deliberate interference. Frequency diversity provides a means of improving the signal to noise ratio of a radar system.

It is, therefore, an object of this invention to provide an improved coaxial magnetron for achieving frequency diversity.

It is another object to improve tuning means for a coaxial magnetron.

It is .another object to provide a small lightweight system for varying the frequency of a coaxial magnetron without substantial addition to the outlying geometry of the magnetron.

In brief, the present invention provides a tuning means within the outer resonant system of the coaxial magnetron which is driven by an electromagnetic system.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of the specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is a top plan view, partially in section, of a coaxial magnetron embodying the present invention, the view being taken along line I-I of FIGURE 2; and

FIG. 2 is a side elevational view, partially in section, and taken along the line IIII of FIGURE 1.

With reference to the drawings, there is shown a coaxial magnetron embodying the present invention. The magnetron is comprised of a body member 10 which is substantially cup-shaped and includes a substantially cylindrical side wall 12 and a bottom plate 14 of a suitable electrically conductive material such as copper. Centrally disposed within the body 10 is a cathode 16 which includes a sleeve member 18 of a suitable material such as molybdenum having an electron emissive coating 20 provided thereon of a suitable material such as barium oxide.

Surrounding the cathode 16 is .a substantially cylindrical anode 22 having a plurality of vanes 24 which extend radially inwardly therefrom. The planes of the anode vanes 24 are inclusive of the axis of the cylindrical anode 22 .and define in cooperation with the anode 22 an array of anode cavity resonators 26. Coupling slots 28 extend through the cylindrical anode 22 and are centered between adjacent anode vanes 24. The coupling slots 28 communicate with alternate ones of the cavity resonators 26.

The cylindrical wall portion 12 of the body 10 and the cylindrical anode 22 along with the bottom portion or plate 14 of the body 10 define, in part, an outter cavity resonator 30. Extending through the wall 12 so as to communicate with the outer cavity resonator 30 is an output coupling slot 32. The coupling slot 32 serves as a means for removal of energy from the outer cavity resonator 30. An output window assembly 33 is associated with the output coupling slot 32 to provide suitable matching and a vacuum type barrier in a well known manner.

Positioned on top of the cup-shaped body 10 is a disk shaped cover means 34. The cover 34 is of a suitable non-magnetic material such as stainless steel and is vacuum sealed at its periphery to the cylindrical wall portion 12. This vacuum seal may be accomplished by a simple brazing operation. An upper pole piece 36 of a suitable magnetic material projects through the cover means 34 as illustrated in the drawings and is vacuum sealed to the aperture in the upper plate 34. A lower pole piece 37 extends through an aperture provided in the lower end plate 14 and is sealed therein. Both pole pieces 36 and 37 are annular in shape and surround a portion of the cathode sleeve 18. The external portion of the magnetic circuit includes two C-shaped magnets 39 secured to the pole pieces 36 and 37. The magnetron assembly may be evacuated through a suitable port and closed off by well known means through the aperture provided in the upper pole piece 36 in a well known manner.

An annular groove 40 is provided in the upper surface of the bottom plate 14 which forms one wall of the cavity resonator 30. A tuning ring 42 is positioned within the groove 40 and is secured at one point 38 by a flexible connection 44 substantially at the same angular position as the output coupling slot 32 with respect to the cavity resonator 30. The tuning ring 42 is also connected to a flexible tab 50 diametrically opposite with respect to the tab 44. The tab 44 is secured to the bottom plate 14 while the tab 50 is secured to a flexible elongated member 52. This elongated member 52 may be of a suitable material such as stainless steel or copper and of a non-magnetic material. The member 52 has a thickness of abaiit .020 inch and a width of about .400 inch. The tuning ring 42 is of a good electrically conductive material such as copper. The ring 42 has a thickness of about .005 inch and a width of about .200 inch. The depth of the groove 40 is about .075 inch or wavelength and the width of the groove is about .250 inch. In the specific embodiment shown, the tuning ring 42 is disposed at substantially equal distances from the outer wall 12 and the wall of the anode 22.

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The elongated member 52 is provided with a suitable driving mechanism. This mechanism is provided within an outer casing 60 of a suitable material such as copper, which extends through the outer wall 12 and the bottom plate 14. The casing 60 is vacuum sealed to the cupshaped portion 10. The elongated member 52 is disposed within the casing 60. One end of the elongated member 52 is secured to the tuning ring 42 and the opposite end of the elongated member 52 is secured to a support portion 62 by means of suitable fastening means such as a screw 64. The elongated member 52 extends through an opening 66 in the side wall 12 and the bottom plate 14 to engage the tab member 50. The opening 66 is adequate to permit movement of the elongated member 52 in a vertical direction. As can be seen from the drawing, the elongated member 52 is secured in a cantilever fashion. Also provided within the casing 60 is a pole piece 68 which extends through an aperture 70 in the elongated member 52. A second pole piece 72, which is substantially cup-shaped, is supported from the pole piece 68 by means of a spacer 74 which is of a non-magnetic material. The two pole pieces 72 and 68 are dimensioned and positioned such that a portion of the pole piece 68 extends into the cup of the pole piece 72.

Secured to the upper side of the elongated member 52 and positioned about the aperture 70 is a sleeve member 76 of a suitable material such as a non-magnetic stainless steel. Around the sleeve 76 there is formed a coil 78 of electrically conductive Wire. The sleeve 76 and the coil 78 are of such length to extend from the elongated member 52 into the cup-shaped pole piece 72. Suitable conductors 80 extend from the coil 78 through the casing 60. The conductors 80 are insulated from casing and are provided with a suitable electrical potential. The two pole pieces 68 and 72 are located within the fringe field of the main magnets 39 which are connected to the pole pieces 36 and 37. This fringing field provides a magnetic field between the pole pieces 68 and 72 which extends radially between the pole pieces 68 and 72.

In operation, the passage of current through the coil 78 which is located within the radial magnetic field will cause movement of the elongated member 52 and in turn movement of the ring 42 tending to tilt the ring 42 as indicated in the dotted lines in FIG. 2. In this manner frequency tuning is achieved when the drive system moves the ring 42 substantially parallel to the axis of the cavity and changes in effect the volume of the cavity. In one specific device in which the operating frequency of the magnetron was 16,500 megacycles raising the ring at the point of driving by an amount of .005 inch resulted in a change in frequency to 16,515 megacycles. By driving the ring below the surface of the wall 14 by a distance frequency was obtained of about 16,485 megacycles.

In the specific device illustrated, the coaxial magnetron is of the tunable type in which a movable tuning member 90 is provided in the upper portion of the cavity. This type of tuning is more fully described in copending application No. 298,775 filed July 30, 1963, now US Patent 3,263,118 and assigned to the same assignee as this invention.

It is also obvious that different means of driving the tuning ring 4 2 could be provided. For example, it might be desirable to have more than one driving unit so that different electrical signals could be utilized for each of the driving units or to obtain greater frequency change. It is also obvious that other tuning configurations for the ring 42 might be incorporated in the cavity.

It is also obvious that a second coil might be provided at some point on the elongated member 52 and as a result of passing through the magnetic field provided by the two main magnets could provide an electrical current therein. This current could be utilized as a feedback monitor signal to amplitude modulate the voltage applied to the coil 78 or utilized to give an indication of the position of the member 52. The natural frequency of the elongated member 52 should be adjusted to approximately the same frequency at which the coil 78 is pulsed.

While there has been shown and described what is at present considered to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to this specific arrangement shown and described, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

I claim as my invention:

1. A coaxial magnetron comprising a centrally disposed cathode, a cylindrical anode including a plurality of anode resonators circularly positioned about said cathode, an outer cylindrical wall surrounding said cylindrical anode, said outer wall and said anode with end walls defining an outer coaxial cavity resonator of substantially annular cross-section, means within said anode for coupling energy from said anode resonators to said outer coaxial cavity resonator, a tuning assembly for said magnetron comprising an assembly including an elongated flexible lever member fixed at one end and free at the other end, a cavity tuning member secured to the free end of said flexible member, said cavity tuning member forming a portion of said outer cavity resonator and means for moving an intermediate portion of said flexible lever member whereby the degree of extension of said tuning member into the cavity of said outer cavity resonator is varied to effect tuning of said coaxial magnetron.

2. The coaxial magnetron of claim 1, in which said cavity tuning member is an annular member located in one of said end walls.

3. The coaxial magnetron of claim 1, said means for moving said flexible member includes magnetic means disposed for effecting a magnetic field substantially parallel to said flexible member and a coil mounted on said flexible member between said fixed end and said free end of said flexible member.

4. The coaxial magnetron of claim 2, in which said annular member is secured at a first point to the free end of said flexible member and secured by flexible means to said cavity resonator at a second point diametrically opposite said first point.

5. The coaxial magnetron of claim 1, in which said tuning means is positioned within a groove in a wall of said cavity resonator.

6. The coaxial magnetron of claim 1 in which said cavity tuning member is located in one end wall and an additional movable tuning member is located adjacent the other end wall.

References Cited UNITED STATES PATENTS HERMAN KARL SAALBACH, Primary Examiner.

S. CHATMON, Assistant Examiner, 

